Several publications and patent documents are cited throughout the specification in order to describe the state of the art to which this invention pertains. Each of these citations is incorporated herein by reference as though set forth in full.
Gene therapy aims to treat both genetic and infectious diseases via introduction of new genetic material into the appropriate cells in the body. One of the greatest challenges of gene therapy is efficient transfer of genetic material into living cells. Use of recombinant viral vectors for gene delivery significantly improved this process. Two commonly used viral vectors capable of direct in vivo gene transfer are derived from adenovirus (Ad) and adeno-associated virus (AAV). The majority of the 987 worldwide gene therapy trials use viral vectors, 256 use Ad vectors (25.9%) and 25 use AAV vectors (2.5%).
A variety of gene delivery vectors have been developed that can achieve delivery of therapeutic genes to mammalian cells in vitro and in vivo. Some of these are viral vectors which are based on common viruses, for example, adeno-associated virus, Type 2 (AAV2). Structurally, AAV2 is a relatively simple virus, is ubiquitous in the human population and is not known to cause disease. Genetically modified (recombinant) AAV2 has been studied extensively as a gene delivery vector with potential to effectively treat many serious and chronic diseases in humans. More recently additional serotypes of AAV, (e.g., AAV8) have been described that further expand the promise of these vectors for therapeutic gene transfer. Studies performed using a number of different animal models have demonstrated that AAV vectors can mediate transfer and expression of genes encoding therapeutic proteins such as blood coagulation factors VIII (Scallan, et al.) and IX (Herzog et al. 1999), Synder et al., (1999) and monoclonal antibodies (Lewis et al. 2002) and several other proteins of potential therapeutic clinical benefit. Human clinical trials in which AAV2 vectors expressing human coagulation factor IX were administered confirmed their ability to deliver therapeutic levels of human coagulation factor IX (High et al. 2003; Manno et al. 2006). However, pre-existing immunity to AAV2, and adaptive immune responses to the non-human components (e.g., viral capsid proteins) of AAV-based gene transfer vectors remains a barrier to achieving consistent and efficient gene transfer and long term expression of therapeutic genes in humans. Studies support that rapid degradation and clearance of AAV capsid protein from transduced cells is important to achieve long-term therapeutic transgene expression in humans.